Abstract Classic is an extension to add to the famous Mozilla Firefox which installs in the browser new icons and neutral colors, rather discreet, in which the ash color stands out, leaving the search bar with soft colors.
Abstract Classic is therefore recommended to people of discreet tastes, possibly adults who do not appreciate stridencies.
The only great drawback of Abstract Classic is that when installing it, the progress buttons disappear, so you have to install them manually (something not difficult, on the other hand) and so you will have the most aesthetically discreet Mozilla Firefox you can imagine.
You can free download Abstract Classic 32, 64 bit and safe install the latest trial or new full version for Windows 10 from the official site.